1. FIELD OF THE INVENTION
The present invention relates to a method of preparing azo dyes, and particularly quinone residue-containing azo dyes.
An azo dye containing a quinone residue in the molecule can be effectively used as an intermediate of a certain kind of dye and a dye developer for the color diffusion transfer process.
2. DESCRIPTION OF THE PRIOR ART
In the art of producing azo dyes, known methods are described in, e.g., U.S. Pat. Nos. 3,086,005, 3,222,169 and 3,307,947. These methods contain the following steps:
A. diazotization of an amine having a hydroquinone residue protected by an acetyl group, that is, a diacetoxy benzene residue, PA1 B. an azo coupling reaction of the resulting diazotized amine, PA1 C. removal of the acetyl group by hydrolysis to form the azo dye containing a hydroquinone residue, and PA1 D. oxidation of the above product to form an azo dye containing a quinone residue. PA1 1. Amino group-containing hydroquinones are reacted with couplers containing a carboxylic acid chloride group, (The reaction of amines with carboxylic acid chlorides is a very common reaction, and is described in mmany scientific references and literature, e.g., Romeo B. Wagner and Harry D. Zook, Synthetic Organic Chemistry, pp. 566 .about. 567, John Wiley & Sons, New York, (1961). Amino group-containing hydroquinones are conventionally well known, and are described, for example, in U.S. Pat. Nos. 3,019,107, 3,236,893 and 3,307,947.), PA1 2. Amino group-containing hydroquinones are reacted with couplers containing a sulfonic acid chloride group, PA1 3. Under the same conditions as those described in U.S. Pat. Nos. 3,246,016, 3,245,790 and 3,288,788, hydroquinones containing homogentisic acid lactones or carboxylic acid chloride groups (wherein hydroxyl groups are protected by acylation or reaction with alkyl chloroformate) are reacted with amino group-containing couplers, and PA1 4. As described in U.S. Pat. No. 3,252,990, hydroquinones containing amino groups which can be diazotized (the hydroxyl groups of which are protected by acylation or by reaction with alkyl chloroformate) are diazotized, reacted with substituted esters of succinic acid, and then, the protecting groups are removed from the hydroquinone moiety. PA1 1. The quantity of the diazonium compound added to the quinone residue-containing coupler should range from about 0.1 to 10 molar equivalents, and preferably from 0.5 to 1.5 molar equivalents, to the diazonium compound. PA1 2. Suitable temperatures for carrying out the reaction should range from about 31 5.degree. C to +15.degree. C., and preferably from 0.degree. C to 5.degree. C. PA1 3. the effective pH range for conducting the reaction should be lower than about 9, and preferably a pH of from 5 to 7. PA1 4. The reaction should be carried out with vigorous stirring.
The above methods, however, possess the following technical disadvantages.
1. An amine having a hydroquinone residue must be acetylated in order to protect the hydroxyl groups of the hydroquinone moiety which may be subjected to oxidation. In addition, the above acetylation reaction must be carried out with greatest care because the amino group must be protected from acetylation.
2. Removal of the acetyl group must be carried out. This reaction must also be achieved carefully because hydroquinone is particularly unstable in an alkaline solution.
3. The amine used in the above methods is converted to an azo dye, to begin with. Then, the resulting azo dye is subjected to both the removal of the acetyl group and an oxidation. Since such an azo dye usually has a lower solubility than the amine which is used as a starting material, because the azo dye has a higher molecular weight, only a few solvents can be used for the synthesis and purification according to the above procedures, and, use of a large amount of solvent, may be required.